1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to power transmission belts having teeth at spaced intervals along the length thereof.
2. Background Art
Toothed belts are used in a number of different industries. In one application, toothed belts are used for the synchronous driving of machine components wherein there is a potentially high load transmission capability required.
Toothed belts often fail primarily for two different reasons. First of all, load carrying/tension members may break due to bending fatigue. Second, rubber that is used to construct the belts may not have adequate resistance to heat encountered in a particular use environment.
To improve the performance of the load carrying/tension members, efforts have been made to improve the quality of the material making up these members. Efforts have also included reducing the diameter of these members to increase their flexibility. Still further, heat resistance of load carrying members has been enhanced by the use of different treatment agents. The heat resistance of the belt rubber may be improved by using different compositions, such as hydrogenated nitrile rubber, etc.
In JP-A 2008-101728, there is a focus on improving the heat resistance of rubber. To achieve this end, hydrogenated nitrile rubber is mixed with an unsaturated carboxylic acid metal salt to define a rubber composition that forms the belt teeth. The disclosed rubber composition is not believed to have either a hardness or modulus that is at an adequate level. As a result, the teeth may be prone to cracking, as demonstrated by running testing performed under high load, before the end of an adequate useful life. More specifically, toothed belts with this composition used with machines in industries that require high load transmission capability tend to be compromised by showing wear at the bottom of the teeth at which loads of a heavy nature are applied. Additionally, cracks may tend to generate at the bottom of the teeth where the aforementioned wearing occurs.
Alternatively, as disclosed in JP-A 2000-27949, a rubber composition is formed by mixing organic peroxide and ethylenically unsaturated carboxylic acid metal salt into a synthetic rubber that has a completely saturated main chain. This rubber is used for the teeth on a belt with the objective of providing good dynamic fatigue resistance. However, since the rubber composition uses a synthetic rubber with a completely saturated main chain, the cross-linking reaction between polymers would appear to be insufficient and, as a result, the teeth may not be made with the necessary stiffness.